6,408 research outputs found
Metric projective geometry, BGG detour complexes and partially massless gauge theories
A projective geometry is an equivalence class of torsion free connections
sharing the same unparametrised geodesics; this is a basic structure for
understanding physical systems. Metric projective geometry is concerned with
the interaction of projective and pseudo-Riemannian geometry. We show that the
BGG machinery of projective geometry combines with structures known as
Yang-Mills detour complexes to produce a general tool for generating invariant
pseudo-Riemannian gauge theories. This produces (detour) complexes of
differential operators corresponding to gauge invariances and dynamics. We
show, as an application, that curved versions of these sequences give geometric
characterizations of the obstructions to propagation of higher spins in
Einstein spaces. Further, we show that projective BGG detour complexes generate
both gauge invariances and gauge invariant constraint systems for partially
massless models: the input for this machinery is a projectively invariant gauge
operator corresponding to the first operator of a certain BGG sequence. We also
connect this technology to the log-radial reduction method and extend the
latter to Einstein backgrounds.Comment: 30 pages, LaTe
Conformal blocks for Galois covers of algebraic curves
We study the spaces of twisted conformal blocks attached to a -curve
with marked -orbits and an action of on a simple Lie
algebra , where is a finite group. We prove that if
stabilizes a Borel subalgebra of , then Propagation
Theorem and Factorization Theorem hold. We endow a projectively flat connection
on the sheaf of twisted conformal blocks attached to a smooth family of pointed
-curves; in particular, it is locally free. We also prove that the
sheaf of twisted conformal blocks on the stable compactification of Hurwitz
stack is locally free.
Let be the parahoric Bruhat-Tits group scheme on the quotient
curve obtained via the -invariance of Weil restriction
associated to and the simply-connected simple algebraic group with
Lie algebra . We prove that the space of twisted conformal blocks
can be identified with the space of generalized theta functions on the moduli
stack of quasi-parabolic -torsors on , when the
level is divisible by (establishing a conjecture due to
Pappas-Rapoport).Comment: 72 pages; This paper supersedes the original version. This is a much
larger version with many more results. In particular, we confirm a conjecture
by Pappas-Rapoport for the parahoric Bruhat-Tits group schemes considered in
our pape
Multisymplectic formulation of fluid dynamics using the inverse map
We construct multisymplectic formulations of fluid dynamics using the inverse of the Lagrangian path map. This inverse map, the ‘back-to-labels’ map, gives the initial Lagrangian label of the fluid particle that currently occupies each Eulerian position. Explicitly enforcing the condition that the fluid particles carry their labels with the flow in Hamilton's principle leads to our multisymplectic formulation. We use the multisymplectic one-form to obtain conservation laws for energy, momentum and an infinite set of conservation laws arising from the particle relabelling symmetry and leading to Kelvin's circulation theorem. We discuss how multisymplectic numerical integrators naturally arise in this approach.</p
Light-Cone Observables and Gauge-Invariance in the Geodesic Light-Cone Formalism
The remarkable properties of the geodesic light-cone (GLC) coordinates allow
analytic expressions for the light-cone observables, providing a new
non-perturbative way for calculating the effects of inhomogeneities in our
Universe. However, the gauge-invariance of these expressions in the GLC
formalism has not been shown explicitly. Here we provide this missing part of
the GLC formalism by proving the gauge-invariance of the GLC expressions for
the light-cone observables, such as the observed redshift, the luminosity
distance, and the physical area and volume of the observed sources. Our study
provides a new insight on the properties of the GLC coordinates and it
complements the previous work by the GLC collaboration, leading to a
comprehensive description of light propagation in the GLC representation.Comment: 25 pages, no figures, published in JCA
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